Hydraulic feeding apparatus for machine tool units



Dec. 1o, 1935.

' E. J. KINGSBURY 2,023,842

HYDRAULIC FEEDING APPARATUS FOR MACHINE TOOL UNITS I Filed July l5, 1932 4 Sheets-Sheet l Dec. 10, 1935. E. J. KINGSBURY HYDRAULIC FEEDING APPARATUS FOR MACHI NE TOOL UNITS Filed July '15,. 1932 4 Sheets-Sheet 2 A A 2.525, A A l Dec. I0, 1935. E J, KlNGsBURY l' I 2,023,842

HYDRAULIC FEEDING APPARATUS FOR MACHINE TOOL UNITS Filed July 15, 41932 4 Sheets-Sheet 3 l IQ l gl! r-` 'I Dec. l0, 1935. l E. J. KINGsBuRY 2,023,842

HYDRAULIC FEEDING APPARATUS FOR MACHINE TOOL UNITS Filed July 15, v)1932 4 Sheets-Sheet 4 l MMM] Patented Dee. To, 193s i UMTED sTATEs HYDRAULIC FEEDING APPARATUS FOB i MACHINE 'EDOL UNITS Edward Joslin Kingsbury, Keene, N. H., assignor to Kingsbury Machine Tool Corporation, Keene, N. H., a corporation of New Hampshire Application July 15, 1932, Serial No. 622,786

14 Claims.

This invention relates to improvements in hy;- draulic feed apparatus for machine tool units, and more particularly concerns an apparatus of this type in which two pistons are employed for accomplishing and controlling the feeding and Withdrawal of a tool with respect to the work.

One of the features of the present invention is the provision of two independent pistons of which one operates in conjunction with its cylinder for accomplishing and controlling the feeding and withdrawal of the tool, while the other operates to determine the feeding and withdrawal movements, and their rate and sequence, in conjunction with the first piston.

Another feature of the present invention is the employement of a large piston for producing the feeding and' withdrawal motion, in conjunction* with a small piston operating as a stop and valve structure for controlling the motion.

A further feature of the present invention is the provision of means for relieving the oil pressure upon the completion of a cycle, whereby to avoid unnecessary or excessive heating ofthe fluid while the feeding system is at rest.

Other features of the invention relate to the specific form, arrangement and construction of the several parts 'and will appear in detail in the following specification and claims.

An illustrative form of practicing the invention is set forth in the accompanying drawings, in which:

Figure 1 is a vertical longitudinal sectional view through a machine tool unit including a hydraulic feeding apparatus according to the present invention.

Figures 2 and 3 are fragmentary similar views, showing other positions of the parts.

Figure 4 is a transverse vertical section substantially on line 4 4 of Figure 1.

Figure 5 is an end elevation of the rear of the unit.

Figure 6 is a horizontal sectional view substantially on line 6-6 of Figure 1.

Figure 7 is a fragmentary vertical longitudinal sectional view'substantially on line 'I-l of Figure 5.

In the drawings, the apparatus is shown as comprising a stationary bed B and a tool structure K which is slidable on the bed in a longitudinal direction thereof, being guided by the giband-key devices shown in Figure 4. This tool structure K comprises a body providing cylinders for the hydraulic pistons, a driving motor M, and a housing H containing the gearing for driving the tool T (illustrated as a drill) and the pump for establishing the hydraulic pressure for the feed apparatus.

The body of the tool structure K provides a small cylinder i0 and a large cylinder II which are co-axially disposed and formed as extensions 5 one of the other. lT'he small cylinder I0 receives a sleeve I2 which is held in fixed position by a set screw I 3, for supporting the smaller piston I4, which has a longitudinal passage I 5 therethrough opening by branch passages at its right hand end 10 (Fig. 1) into the cavity of the large cylinder II, and provided at lits right hand end'with a projecting pin I6. The left `hand end of the small piston is provided with a peripherally projecting stop ange I1 for engaging the left hand 15 wall of the bushing I2. Longitudinal grooves I8 are provided in the small piston I4 and ange I'I, these grooves being of greater length than the bushing I2 so that they establish communication along the length of the piston when the 20 llatter is in its right hand position. The left hand end of the small piston I4 also has a cavity to receive a ball check valve I9 and its retaining spring 20, these parts being held in position by an apertured end plug 2l, and serving to prevent 25 passage of uid through the central channel I5 of the piston I2, from left to right.

The large piston 22 is illustrated as integral with a. piston rod 23 of lesser diameter which extends through 'a correspondingly-diametered 30 passage 2l co-axial with the two cylinders, and

' being provided at its end with a clamping and stop piece 23. An internally threaded cavity 26 in the right hand end of piston rod 23 engages with a screw 2l revolubly lmounted in an up- 35 standing bracket 23 of `the bed B, and provided with a knob 29 by which it may be revolved.

A packing 33 is provided to prevent the escape of oil from" the right hand end of the large cylinder I I. The piston 22 and its rod 23 have a recess 40 at the left hand end for containing the ball check valves 3l, 32 which are actuated in opposite directions by a single spring 33 and serve to obstruct the passage of oil through the apertured end closing plug 3i and the-transverse 45 escape channels 35. Longitudinal grooves 36 are provided from the left hand face of the large piston 22 to a point beyond the escape channels 35. A

A threaded spindle 31 is rotatably mounted in 50 an aperture of the front face of the housing H and provided with a collar 33 and a head 39 engageable by a spanner wrench or a. like tool for rotating the spindle. The right hand threaded end or spindle 31 extends through an externally 56 threaded closing plug 49 for the small cylinder I0.

The motor M operates through a universal connection 45 to drive a shaft 46 having a, gear 41 thereon in mesh with a gear 48 on a back shaft 49 having a gear 50 in mesh with a gear 5| on the tool shaft 52. Thus the motor M may drive the tool at a speed determined'by the ratios of the gears 41`-48'and 50-5I. Back shaft 49 is provided with an extension connected with lthe upper gear 53 of a gear pump having a lower gear 54 and a housing 55, and provided with a suction connection 56 from a sump in the lower part of the tool structure K and a delivery pipe 51 leading (Fig. 6) to a. longitudinal passage 58 in the body of the tool structure K, and opening into a transverse fluid passage 59 having an enlarged portion 60 at its outer end (Figs. 4 and 6) containing a sliding valve 6| held inwardly by a spring 62 which may be adjusted by the screw 63 held by the closing plug 64, and operating normally to close the discharge passage 60a. The inner end of passage 59 opens into a longitudinal valvepassage 65 having a fixed valve sleeve 66 therein with an opening opposite the passage 59 (Figs. 4 and 6), and containing a valve plunger 61 having a longer reduced portion 68 and a short reduced portion 69 separated by a collar 10, the short reduced portion 69 being closed off in the valve sleeve 66 by a collar 1I. A central longitudinal passage 12 in the valve plunger 61 opens to the'. left hand end of the plunger and to the space provided by the reduced portion 69. A coil spring 13 constantly urges the valve plunger toward the right in the figures, and is contained within a reduced extension of the valve passage 65, which has an extension 14 discharging back y into the sump of thebody of the tool structure K. The valve plunger 61 may be moved manually toward the left in the gures by a crank lever 15 mounted by a pivot 1 6 on the tool structure and having a depending nose 11 directly engaged with the right handv end of the valve plunger 16. A plunger spring 18 moves the crank lever 15 in a counter-.clockwise direction and normally holds it in the positions shown in Figures 1, 2, and 3.

When the valve plunger is in the .extreme right hand position (Fig. 1) the space surrounding the longer reduced portion 68 communicates by a short passage with the right hand end of the large cylinder I I, and the space surrounding the shorter reduced portion 69 communicates by a passage 8| and the longitudinal passage 82 and the passage 83 with the lef-t hand end of the small cylinder I Il. When the plunger is moved to its right hand position (Fig. 2), the passage 8| is in communication with the space surrounding the longerreduced portion 68 of the plunger valve 61, whilethe passage 88 is cut off.

A transverse shaft 90 carries a latch -piece 9| (Figs. 1, 2, 3,'and 5) which may rock in a counter-clockwise direction from the position of Fig'. l into the position of Fig. 2, when thelvalvev plunger -is moved to its left hand position iand ,thus prevent the return movement of the valve plunger. 'I'he shaft 98 is provided with teeth 92 in mesh with teeth 93 on an apertured swinging arm 94 mounted by pivot 95V on the tool structure, and by its aperture embracing the control rod 95 between the two collars 96 thereon. Thejace, under the differential of pressures exist- Aing between the two faces of the piston 22.

contained within the threaded bushing 99. A stop |00 `is provided on the control rod 95 for determining the movement of the control rod, and its'limit of travel.

A transverse passage I|0 opening from the 5 large cylinder II at its right hand end communicates with a larger passage III containing a hollow internally threaded plug II2 providing a needle valve passage I|3 which may be regulated from the exterior by a threaded and adjustable 10 needle valve I I4 (Fig. 4) with a permitted escape of the liquid passing this needle valve through passages |I5 back to the machine sump.

The operation of this hydraulic feed apparatus is as follows: 15

With the parts adjusted to cause the sev'eral movements at the desired points of travel, and assuming that the tool has been. entirely withdrawn from the work and hence is in its extreme right hand position, corresponding to Figure 1, 20 the rotation of the motor M causes an operation of the pump 53, 54, 55 and a delivery of uid under pressure into thev longitudinal passage 58. This fluid is regulated 'in its maximum pressure by the operation of valve 6| and spring 62, so 25 that upon exceeding a predetermined pressure, the fluid may escape back to the sump through the opening 66a. In the position of Figure 1, however, this iluid may pass through channel 59 to the space surrounding the longer reduced portion 30 68 of the valve plunger 61, into the right hand end of the large cylinder I I, and operate to maintain the tool structure K in its right hand moved position. At this time, however, the check valve f 32 is being held open by the pin I6 on ,the small 35 piston I4, so that the iluid in the right hand end of the large piston II may open the spring check valve 3|, and flow past the open valve 32 into the left hand end of the large cylinder I I and thence by the branch passages into the longitudinal passage I5 of the small piston I4, past the check valve I9 thereof, to the left hand end of the small cylinder I0 and thence by passages 83, 92, and 8| to the space around the shorter reduced portion 69, 'and by the passage 12 therein to passages 14 and 45 thus back to the sump. Ihus a constant circulation of oil through the cylinders and relief valves 3| and |9 and control valve plunger 61 can occur to avoid overheating while the device is resting in its extreme withdrawn or returned position.

When an article of work is in position to be operated upon, the attendant momentarily depresses the crank lever 15. The nose 11 moves the valve plunger 61 to its extreme left hand position, until the latch piece 9| snaps behind it. 55 These parts are now in the position of Figure 2. Fluid from the longitudinal passage 58 still continues to pass into the space surrounding the longer reduced portion 68, but now moves through passages 8|, 82, 83 to the left hand end of the small cylinder I0 and thus operates against the left hand end of the small piston I4, producing a bodily leftward movement of the tool structure K by the reaction ofthe fluid under pressure. The uid at the right of the piston 22 can force 65 the'check valve 3| open, as the cylinder moves toward the left; and since pin 'I6 is now holding the check valve 32 open, the iluid can move from the right-hand face of piston 2?. to. the left-hand The cross section of the piston lil and the piston rod 23 are shown illustratively as of substantially 'the same area. The two pistons remain in fixed abutting relationship. This produces a rapid pre- 15 liminary feeding movement of the tool until it attains a close proximity to the work At the end of this predetermined approach movement the peripheral flange I1 on the small piston I4 engages the sleeve I2 and further relative movement between the tool structure K and the small piston I4 is prevented. At this time, however, the longitudinal passages I8 have established communication between the left hand end of the small cylinder and the. left hand end of the large cylinder I I so that the continued flow of` fluid into the cylinder I is accompanied by a passage of the fluid into the left hand end of the large cylinder II and a pressure thereof against the left hand face of the large piston 22 and its rod 23, which are held in a fixed position relative to the bed by the adjustment of the threaded spindle 21. Hence the tool structure K continues to move in a feeding direction, but owing to the reduced size of the passages I8, and the fact of the presence of oil in the right hand end of the large cylinder I I owing to the closure of the passage 80 by the valve plunger 61, this movement is slow. The oil content within the right hand end of the large cylinder Il can only escape through the lateral passage IIB and past the needle valve Il at arate controlled by this needle valve, since the pressure in the longitudinal channel 58 is maintained at a contant maximum by the operation of the valve 6I (Figs. 4 and 6). Hence a slow feeding of the tool occurs while the work is being operated upon by the tool. During the rst portion of this movement, the tool structure K draws the small piston I4 away from the large piston 22, so that the pin I6 withdraws from the valve 32 and permits the latter to close to accomplish the aforesaid `sealing of the right hand end of the large cylinder II.

At the close of this feeding movement the tool structure and pistons are in the relative position shown in Figure 3. 'Ihe movement of the tool structure has carried the control rod 95 therewith untilthe collar Illa has engaged the limit and clamping piece 25, the relationship of these parts being shown in Figures and 6, so that the final movement leftward of the tool structure K has resulted in a stoppage and retaining of the control rod 95 against the action of spring 96, so that the arm 94-is rocked and its teeth 93 cause a movement of teeth 92 and a movement of the latch piece SI in a clockwise direction, so that the plunger 61 is liberated and is returned to its right hand position'. by the spring 13. Communication is vthus established from longitudinal passage 58 past the longer reduced portion 68 to passage 80 and thus to the right hand end of the larger cylinder II: while the longitudinal passage 82 is again placed in communication (Figs. 1 and 3) with the space around the shorter reduced portion 69. Fluid now ows through the passage 80 and causes a reaction between the right hand face of the large piston 22 and the right hand end wall of the large cylinder II, so that the tool structure K is drawn rapidly back in a rightward position to withdraw the tool from the work. During the preliminary portion of this iiow, the check, valve I9 and the friction in passages I5 and I8 impose a resistance to the ow of the fluid from the right hand face to the left hand face of the small piston I4, and by reason of the pressure differentials at the ends of this small piston Il, it is moved relative. to

its cylinder (relatively toward the leftfrom the position of Fig. 3). A short travel of piston I4 closes the passages I8, so that a greater resistance is opposed to the ow of the uid from the left-hand end to the large cylinder back to the sump, as all of the fluid must now pass through the passage I5 and by the valve I9. 'I'he result is a rapid return of the piston Il until it is 5 stopped by the spindle 31, and thereafter the valve I9 continues to permit the escape of fluid from the left hand end of the cylinder II. It will be understood, however, that the frictional and valve resistances opposed to this flow of fluid 10 is much lower than the resistance provided by the needle valve I I4, s o that the full discharge of the pump into the right-hand end of the cylinder II is not resisted by a high back pressure opposed to the escape from the left-hand end (as was the reverse case during the slow forward feeding) nor does the small ow through the passage H0 predominate, and thus the return movement of the tool body toward the right occurs at a rapid rate. Finally, the pin IB is brought against the valve 32 and opens this valve,

so that fluid can now pass from the right-hand end of cylinder II, past the check valve 3|, past the open valve 32, through the left-hand end of cylinder II, through passage I5 and past valve 25 I9, and thus by passages 83 and 82, etc. back to the sump. Thus, ultimately, the two pistons are restored to the relative position shown in Figure 1 and the free circulation of the pressure medium is permitted. In adjustment it will be noted that the position of the threaded spindle 31 determines the left hand position of the small piston I4 relative to the tool structure K, and hence the position of the tool structure K with respect to bed B when'the tool is Withdrawn from 35 the work. Similarly, the large piston 22 when present at the right hand'end of its cylinder determines the farthest advance of the tool toward or into the work, and this position may be regulated with respect to the bed B by the adjustment of the threaded spindle 21. Since the piston rod 23 carries the clamping 'and limit piece 25, it normally is unnecessary to adjust the collar |00 in passing from one distance of travel to another, but an adjustment thereof may be made todetermine the relative sensitiveness of the device in responding to varied conditions.

It is obvious that the invention is not limited to the form of embodiment shown, but that this may be modified in many ways within the scope of theappended claims.

Having thus described the invention, what I claim as new and desire to secure by Letters Patent, is:

1. A machine tool unit includinga tool operating by reciprocating action, a frame, a tool supporting body reciprocable relative to said frame, said body having cylinders, independent first and second pistons in said cylinders adapted to abut one against another in the withdrawn position of said body, a source of uid under pressure, a manually operable spring valve adapted in one position to permit the passage of duid from said source to one end of the first piston whereby to produce a rapid approach feeding of the tool to65 the work, meansfor limiting the relative movement of said first piston in its cylinder, a bypass controlled by said first piston and opened in the limit position thereof to permit the passage of fluid to one side of said second piston whereby to continue the feeding movement of the tool, a detent for holding said valve in said feeding 'position during the feeding movement of the tool, means operated` by the body at the end i I of its feeding movement for releasing said de- 3. A machine tool unit including a tool operated by reciprocating action, a frame, a tool supporting body reciprocable relative to said frame and including cylinders, first and second pistons in said cylinders, valve means for selectively admitting fluid to one end of one said piston and to the other end of the other said piston, one of said pistons having an axial passage therein from one end to the other, check valves for preventing passage of fluid in either direction in said passage, and means on the other piston for moving one said check valve from its seat.

4. A machine tool unit including a tool operating by reciprocating action, a frame, a tool supother said cylinder, and a restricted outlet for "i fluid from the end of the larger cylinder to which fluid may be admitted by said valve means, whereby the admission of fluid into said smaller cylinder produces a rapid forward feeding movement during which fluid may flow from one face of the larger piston to the other through the check valve of the passage of said piston; said smaller cylinder and piston including means for the delivery of fluid to said larger cylinder when said smaller cylinder and piston are in a predetermined relative position, fluid being permitted from the opposite face of said larger piston through said restricted outlet for a slow for'- ward feeding, said valve means also selectively controlling the admission of fluid to said restricted outlet end of the larger cylinder for producing a rapid return movement of the body relative to the frame with an escape of fluid through the check valve of said smaller piston.

5. A machine tool unit including a tool operating by reciprocating action, a frame, a tool supporting body reciprocable relative to said frame and including coaxial cylinders, two independent pistons movable in said cylinders, each said piston having an axial passage from one end to the other, check valves for closing said passages against movement of iluid therethrough during the forward movement of the tool body relative to the frame, a second check valve in one said piston for preventing movement of fluid past the same during the withdrawal movement of the tool body, means connecting said one piston to the frame, a source of fluid under pressure, valve means for selectively controlling the admission of fluid to one end of one said piston and to the other end of the other said piston, and means on the other said piston for relieving said second check valve during an initial feeding movement of the body. 6. A machine tool unit including a tool operating by reciprocating action, a frame, a tool supporting body reciprocable relative to said smaller cylinder and piston including means for the delivery of fluid to said larger cylinder when said smaller cylinder and piston are in a prede- 10 I termined relative position, a check valve for closing said passage in the larger piston against movement of fluid therethrough, a source of fluid under pressure, and valve means for selectively controlling the admission of fluid to one end of 15 one said piston and to the other end of the other said piston.

7. A machine tool unit including a tool operating by reciprocating action, a frame, a tool supporting body reciprocable relative to said 20 frame and having a vpair ofv coaxial cylinders, two independent pistons in said cylinders adapted to abut against one another in the withdrawn position of the body, a source of fluid under pressure, valve means for selectively admitting'fluid to one end of one said piston whereby to produce an initial feeding movement of -the body toward the work, means to limit the movement of said one piston, means controlled by said one piston for preventing the passage of fluid 30 to said other piston during the initial feeding and operating when the said one piston is in limit position for permitting such passage whereby said other piston causes a further feeding movement, said valve means also operating to admit fluid to the other side of said other piston whereby to produce a, withdrawal movement of the body, and cooperating devices on said pistons for preventing the passage of fluid from one side of said other piston to the other while said pistons 40 are separated and for permitting such passage when said pistons are in abutting relationship.

8. A machine tool unit including a tool operating by reciprocating action, a frame, a tool supporting body reciprocable relative to said frame and including coaxial communicating smaller and larger cylinders, smaller and larger pistons in said cylinder, means for connecting said larger piston to the frame against relative movement with respect thereto, a source of fluid under pres- 50 sure, valve means for selectively admitting fluid l to the end of said smaller cylinder which is remote from said larger cylinder for producing the forward feeding of the b'ody relative to the frame and to the end of said larger cylinder which is remote from said smaller cylinder for the return of said body relative to the frame, said smaller cylinder and piston including' means for passing fluid fromcne face of said smaller piston to the other upon a predetermined forward feeding movement whereby to deliver fluid to the end of said larger cylinder adjacent said smaller cylinder for a flne continued forward feeding movement, said larger cylinder and piston including a passage for fluid from one face of 65 said larger piston to the other and a device for normally closing said passage and operated by said smaller piston during said predetermined feeding movement for permitting the passage of fluid through said passage, and a restricted out- 70 let for controlling the escape of fluid from the end of said larger cylinder remote from the smaller ,cylinder whereby to control the fine forward feeding` 9. A machine tool unit including a tool operatlto the other, check valves for closing said pasing by reciprocating action, a frame, a tool supporting body reciprocable relative to said frame and including coaxial communicating smaller and larger cylinders, smaller and larger pistons in said cylinder, means for connecting said larger piston to the frame against relative movement with respect thereto, a source of fluid under pressure, valve means for selectively admitting fluid to the end of said smaller cylinder which is remote from said larger cylinder for producing the forward feeding of the body relative to the frame and to the end of said larger cylinder which is remote from said smaller cylinder for the return of said bodyrelative to the frame, said smaller cylinder and piston includingmeans for passing iluid from one face of said smaller piston to the other upon a predetermined forward feeding movement whereby to deliver fluid to the end of said larger cylinder adjacent said smaller cylinder for a ne continued forward feeding movement, said larger cylinder and piston including a passage for fluid from one face of said larger piston to the other and a device for normally closing said passage and operated by said smaller piston during said predetermined feeding movement for permitting the passage of fluid through said passage, a restricted outlet for controlling the escape of fluid from the end of said larger cylinder remote from the smaller cylinder whereby to control the ilne forward feeding, said smaller piston having a passage therethrough, and a check valve for closing said passage against the movement of fluid therethrough during the feeding movement of the tool body but permitting the movement of fluid therethrough when` said valve means permits the passage of fluid from one face of said larger piston to the other whereby a ow. of fluid may continue lthrough said cylinders in the withdrawn position of the body relative to the frame.

10. A machine tool unit including a tool operated by reciprocating action, a frame, a tool supporting body reciprocable relative to said frame and having first and second cylinders, independent rst and second pistons in said cylinders, means forlimiting the movement of said rst pistonin each direction relative to the body, means for limiting the movement of said body relative to said second piston in one direction, means for connecting said second piston to the frame, said body being limited in movement in the other ldirection relative to said second piston by abutment of said pistons, a source of fluid under pressure, selective valve means for admitting fluid from said source to one end of said lrst cylinder whereby to feed said body rapidly by reaction through both said pistons in abuttingrelationship, means controlled by said first piston and opera'- tive when said first piston is at the limit of movement relative to said body for establishing a passage for fluid into one end of said secondycylinder to cause the separation of said pistons and to produce a further and slow feeding movement, and a device on said rst piston to establish a passage for fluid from one face of said second piston to the other while the pistons are in abutting relationship, said selective valve means being operative also for admitting fluidto the other end of said second cylinder to produce a withdrawal movement. of said body.

11. A machine tool unit including a frame, an element reciprocable relative to the frame and including two coaxial communicating cylinders.

separate pistons in said cylinders, each said piston having a passage from one face thereof sages against'movement of fluid therethrough,

a source of fluid under pressure, and valve means for selectively controlling the admission of fluid to one end of one said cylinder and to the other 5 end of the other said cylinder, means for connecting one'lof said pistons to said frame, said pistons including interengaging portions so that the other said piston may operate through saidone piston to produce -a relative movement of said 10 frame and elem'ent in one direction, and for opening the check valve of said one'piston at a predetermined relative position of said pistons.

12. A machine tool unit comprising a frame and a body reciprocablev relative to said frame, a pisl5 ton connected to said frame, said body including a shaft including a tool holder, a liquid pump, a liquid sump, a motor for continuously driving said shaft and pump, means for providing a cylinder for said piston, a selective control valve for pass- 20 ing liquid from 'said pump to one end of said cylinder for producing vforward traverse and feeding movements of said body relative to said frame and to the other end of said cylinder for producing a return movement of the body, a con- 25 duit and means for restricting the same for permittingthe regulated escape of liquid from said other end of said sump during the forward feeding, a conduit from said valve to the sump for permitting the escape of liquid lfrom said one end 30 during the return movement, means providing a passage from one end of the cylinder to the other, first and second check valves for closing said passage and means for presenting said check valves in closing position and permitting move- 35 ment thereof independently of one another, a rst said check valve being presented by said presenting means to hold said passage closed against the pressure of uid admitted for forward movement, a second said check valve being presented 40 by said presenting means to prevent ow past the same when iluid is admitted for the return movement, and a second piston member operated by the fluid on its way to and from said one end of the cylinder for opening said second check valve to 45 permit flow through said passage for an initial rapid forward movement and to permit flow` through said passage when said body is in its withdrawn position relative tosaid frame.

13. A machine tool unit including a tool op- 50 erating by reciprocating action, a frame, a tool supporting body reciprocable relative to said, frame, piston and cylinder members, one of said members being fixed to the frame and the other said member fixed to the body, said piston mem- 55 ber having a rst passage extending from one face to the other, a `source of fluid under pressure, a manually operable control valve to admit fluid from said source to one end of said cylinder member for producing the forward movements 30 of said body, a detent to hold the control valve in such feeding position, means controlled by the tool body in its forward movement to release said detent whereby the control valve is moved to effect a flow of fluid to the other end of said o5 cylinder member for the return movement of the body, double check valves for normally closing said rst passage during the ilow to either end of the cylinder member, a vsecond piston member operated by the body in its return movement for 70 opening one of said check valves and permitting the free flow of fluid through said valves and the cylinder member from the outlet to the inlet of said source when the structure is in fully returned position, means providing a second pasf'.

sage bypassing said second piston member, and

a check valve in said second passage for closingl xed to the frame and the other said member l fixed to said element, a source of iiuid under pressure, a conduit including a control valve movable into a iirst position for admitting iluid from said source to one end of said cylinder member for producing a forward movement of said element in one direction relative to said frame, a detent for holding the control valve in said iirst position, means actuated upon a predetermined relative movement of the members for releasing said detent whereby to permit the control valve to move into a second position for effecting the passage of fluid to the other end of said cylinder whereby to produce a. relative movement of the element and body in the opposite direction for withdrawal, means providing-a rst passage between the faces of the piston, double check valves in the piston for closing said rst passage when iiuid is being admitted to either end of the cylinder, a second piston member operated by the iiuid and operative during such withdrawal movement for opening one oi' said checkx valves for permitting the free ow of uid through said cylinder and valves when the element is in a predetermined withdrawn position relative to the frame, said second piston memberv having a second passage therein, and a third check valve for closing l5 said second passage during the forward movement.

EDWARD JOSLIN KINGSBURY. 

